The Moist Static Energy Budget in NCAR CAM5 Hindcasts during DYNAMO

The Dynamics of the MJO (DYNAMO) field campaign took place in the Indian Ocean during boreal fall and winter of 2011-2012 to collect observations of Madden-Julian Oscillation (MJO) initiation. Hindcast experiments are conducted with an atmospheric general circulation model with varying values of a dilute CAPE entrainment rate parameter for the first two MJO events of DYNAMO from 01 October – 15 December 2011. Higher entrainment rates better reproduce MJO precipitation and zonal wind, with RMM skill up to 20 days. Simulations with lower entrainment rapidly diverge from observations with no coherent MJO convective signal after 5 days, and no MJO predictive skill beyond 12 days. Analysis of the tropical Indian Ocean column moist static energy (MSE) budget reveals that the simulations with superior MJO performance exhibit a mean positive MSE tendency by vertical advection, inconsistent with reanalysis that indicates a weak negative tendency from vertical advection. All simulations have a weaker MSE tendency due to the net MSE source, and weaker cloud-radiative feedbacks. The gross moist stability (GMS) is used to interpret these MSE budget results in a normalized framework relevant to moisture mode theory. Simulations with larger entrainment are characterized by negative effective GMS, indicating a favorable condition to destabilize a moisture mode in which convection and associated divergent circulations have a net moistening effect on the column. However, this is achieved by excessively strong moistening by vertical MSE advection that compensates for surface flux and cloud radiative feedbacks that are too weak.